With regards to cellular communications networks, interest in deploying low-power nodes (e.g., pico base stations, Home eNodeBs (HeNBs), relays, Remote Radio Heads (RRHs), etc.) for enhancing macro network performance in terms of network coverage, capacity, and service experience of individual users has been constantly increasing over the last few years. At the same time, there is a need for enhanced interference management techniques to address new interference issues resulting from these low-power nodes such as, for example, interference caused by a significant transmit power variation among different cells and interference caused by existing cell association techniques, which were developed for more uniform cellular communications networks.
In 3rd Generation Partnership Project (3GPP), heterogeneous network deployments have been defined as deployments where low-power nodes of different transmit powers are placed throughout a macro cell layout. This also implies non-uniform traffic distribution. Heterogeneous network deployments are, for example, effective for capacity extension in certain areas, which are often referred to as traffic hotspots. The traffic hotspots are more specifically small geographical areas with high user density and/or high traffic intensity where installation of low-power nodes can be deployed to enhance performance. Heterogeneous network deployments may also be viewed as a way of densifying networks to adapt for traffic needs and the environment. However, heterogeneous network deployments also bring new challenges for which the cellular communications network has to be prepared to ensure efficient network operation and superior user experience. Some of these challenges are related to increased interference in the attempt to increase small cells associated with low-power nodes, which is known as cell range expansion. Other challenges are related to potentially high interference in the uplink due to a mix of large and small cells.
More specifically, as illustrated in FIG. 1, according to 3GPP, a heterogeneous cellular communications network 10 includes a number of macro, or high-power, base stations 12 forming a macro cell layout and a number of low-power base stations 14 placed throughout the macro cell layout. For Long Term Evolution (LTE), the macro base stations 12 are referred to as Evolved Node Bs (eNBs). The low-power base stations 14 are sometimes referred to as pico base stations (serving pico cells), femto base stations (serving femto cells), HeNBs, or the like. Interference characteristics in a heterogeneous network deployment, such as the heterogeneous cellular communications network 10, for the downlink, uplink, or both the downlink and the uplink can be significantly different than in a homogeneous deployment.
Some examples of new interference scenarios that may be present in the heterogeneous cellular communications network 10 are illustrated in FIG. 1 and are indicated as interference scenarios (A), (B), (C), and (D). In interference scenario (A), a User Equipment (UE) 16 is served by the macro base station 12 and has no access to a nearby Closed Subscriber Group (CSG) cell served by one of the low-power base stations 14. As a result, downlink transmissions by the low-power base station 14 for the CSG cell will result in downlink interference at the UE 16. In interference scenario (B), a UE 18 is served by the macro base station 12 and has no access to a nearby CSG cell served by one of the low-power base stations 14. As a result, uplink transmissions by the UE 18 result in severe uplink interference towards the nearby low-power base station 14. In interference scenario (C), a UE 20 connected to a first CSG cell served by one of the low-power base stations 14 receives downlink interference from another low-power base station 14 serving a second CSG cell. Lastly, in interference scenario (D) a UE 22 is served by a pico cell of one of the low-power base stations 14 and is located in an expanded cell range area (i.e., a Cell Range Expansion (CRE) zone) of the pico cell. In this case, the UE 22 will receive higher downlink interference from the macro base station 12. Note that while CSGs are used in many of the examples above, a heterogeneous network deployment does not necessarily involve CSG cells.
Another challenging interference scenario occurs with cell range expansion. With cell range expansion, the traditional downlink cell assignment rule diverges from the Reference Signal Received Power (RSRP)-based approach, e.g. towards path loss or path gain based approach, e.g. when adopted for cells with a transmit power lower than neighbor cells. The idea of the cell range expansion is illustrated in FIG. 2, which generally illustrates a macro base station 24 and a pico base station 26. As illustrated, cell range expansion of a pico cell served by the pico base station 26 is implemented by means of a delta-parameter. A UE 28 can potentially see a larger pico cell coverage area when the delta-parameter is used in cell selection/reselection. The cell range expansion is limited by the downlink performance since uplink performance typically improves when the cell sizes of neighbor cells become more balanced.
To ensure reliable and high bitrate transmissions as well as robust control channel performance, a good signal quality must be maintained in a cellular communications network. The signal quality of a signal received by a receiver is determined by a received signal strength for the signal and a relation of the received signal strength to a total interference and noise received by the receiver. A good network plan, which among other things also includes cell planning, is a prerequisite for successful network operation. However, the network plan is static. For more efficient radio resource utilization, the network plan has to be complemented by at least semi-static and dynamic radio resource management mechanisms, which are also intended to facilitate interference management, and more advanced antenna technologies and algorithms.
One way to handle interference is to, for example, adopt more advanced transceiver technologies, e.g. by implementing interference cancellation mechanisms in UEs. Another way, which can be complementary to the former, is to design efficient interference coordination algorithms and transmission schemes in the cellular communications network. The coordination may be realized in a static, semi-static, or dynamic fashion. Static or semi-static schemes may rely on reserving time-frequency resources (e.g., a part of the bandwidth and/or time instances) that are orthogonal for strongly interfering transmissions. Dynamic coordination may be implemented by, for example, means of scheduling. Such interference coordination may be implemented for all or specific channels (e.g., data channels or control channels) or signals.
Specifically, for heterogeneous network deployments, enhanced Inter-Cell Interference Coordination (eICIC) mechanisms have been standardized for ensuring that the UE performs at least some measurements (e.g., Radio Resource Management (RRM), Radio Link Management (RLM), and Channel State Information (CSI) measurements) in low-interference subframes of the interfering cell. These mechanisms involve configuring patterns of low-interference subframes at transmitting nodes (and thereby reducing interference) and configuring measurement patterns for UEs (and thereby indicating to the UEs low-interference measurement occasions).
Two types of patterns have been defined for eICIC in LTE Release 10 to enable restricted measurements in the downlink, namely: (1) restricted measurement patterns, which are configured by a network node and signaled to the UE, and (2) transmission patterns (also known as Almost Blank Subframe (ABS) patterns), which are configured by a network node, that describe the transmission activity of a radio node and may be exchanged between radio nodes.
Regarding restricted measurement patterns for the downlink, restricted measurements for RRM (e.g., RSRP/Reference Signal Received Quality (RSRQ)), RLM, CSI, as well as for demodulation are enabled by Radio Resource Control (RRC) UE-specific signaling of the following pattern sets to the UE as specified in 3GPP Technical Specification (TS) 36.331 V10.1.0:                Pattern 1: A single RRM/RLM measurement resource restriction for the serving cell,        Pattern 2: One RRM measurement resource restriction for neighbor cells (up to 32 cells) per frequency (currently only for the serving frequency), and        Pattern 3: Resource restriction for CSI measurement of the serving cell with two subframe subsets configured per UE.A pattern is a bit string indicating restricted and unrestricted subframes characterized by a length and periodicity, which are different for Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) (40 subframes for FDD and 20, 60, or 70 subframes for TDD). Restricted measurement subframes are configured to allow the UE to perform measurements in subframes with improved interference conditions, which may be implemented by configuring ABS patterns at the appropriate base stations.        
In addition to RRM/RLM, Pattern 1 may also be used to enable UE Receive (Rx)−Transmit (Tx) measurements in low-interference conditions or in principle for any Cell-Specific Reference Signal (CRS)-based measurement to improve the measurement performance when strong interference may be reduced by configuring low-interference subframes. Pattern 3 would typically be used for enhancing channel quality reporting and improving the performance of channel demodulation and decoding (e.g., of data channels such as Physical Downlink Shared Channel (PDSCH) and/or control channels such as Physical Downlink Control Channel (PDCCH), Physical Control Format Indicator Channel (PCFICH), and Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel (PHICH)). Pattern 1 and Pattern 2 may also be used for enabling low-interference conditions for common signals (e.g., Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS)), common channels, and broadcast/multicast channels (e.g., Physical Broadcast Channel (PBCH)) when strong interference can be reduced or avoided (e.g., when a time shift is applied to ensure that the common channels/signals are interfered with by data transmissions whose interference may be avoided by configuring low-interference subframes and thereby suppressing the interfering data transmissions).
An ABS pattern indicates subframes when a base station restricts its transmissions (e.g., does not schedule transmissions or transmits at a lower power). The subframes with restricted transmissions are referred to as ABS subframes. In the current LTE standard, base stations can suppress data transmissions in ABS subframes, but the ABS subframes cannot be fully blank, i.e., at least some of the control channels and physical signals are still transmitted. Examples of control channels that are transmitted in ABS subframes even when no data is transmitted are PBCH and PHICH. Examples of physical signals that have to be transmitted, regardless of whether the subframes are ABS or not, are CRS and synchronization signals (PSS and SSS). Positioning Reference Signals (PRS) may also be transmitted in ABS subframes. If a Multicast-Broadcast Single-Frequency Network (MBSFN) subframe coincides with an ABS subframe, the subframe is also considered as an ABS subframe, as specified in 3GPP TS 36.423. CRS are not transmitted in MBSFN subframes, except for the first symbol, which allows for avoiding CRS interference from an aggressor cell to the data region of a measured cell. ABS patterns may be exchanged between base stations (e.g., via base station to base station communication, which is referred to as X2 communication in LTE). However, in LTE, the ABS patterns are not signaled to the UE.
In LTE Release 11, for enhanced receivers (e.g., receivers capable of performing an interference handling technique), information about a strongly interfering cell (also known as an aggressor cell) may be provided to facilitate handling of strong interference generated by transmissions in that cell. More specifically, the following information about the interfering cells may be provided to the UE: Physical Cell Identify (PCI), number of CRS antenna ports, and MBSFN subframe configuration. In particular, LTE Release 11 defines the information that may be provided to a UE about an interfering, or aggressor, cell as:
NeighCellsCRS-Info-r11 ::=CHOICE {   releaseNULL,   setupCRS-      AssistanceInfoList-r11}CRS-AssistanceInfoList-r11 ::= SEQUENCE (SIZE (1..   maxCellReport)) OF CRS-AssistanceInfoCRS-AssistanceInfo ::= SEQUENCE {   physCellId-r11PhysCellId,   antennaPortsCount-r11ENUMERATED      {an1, an2, an4, spare1},   mbsfn-SubframeConfigList-r11MBSFN-      SubframeConfigList}
In Universal Mobile Telecommunications System (UMTS)/High Speed Downlink Packet Access (HSDPA), several interference aware receivers have been specified for the UE. These interference aware receivers are referred to as “enhanced receivers” as opposed to the baseline receiver (rake receiver). The UMTS enhanced receivers are referred to as enhanced receiver type 1 (with two branch receiver diversity), enhanced receiver type 2 (with single-branch equalizer), enhanced receiver type 3 (with two branch receiver diversity and equalizer), and enhanced receiver type 3i (with two branch receiver diversity and inter-cell interference cancellation capability). The enhanced receivers can be used to improve performance, e.g. in terms of throughput and/or coverage.
In LTE Release 10, enhanced interference coordination techniques have been developed to mitigate potentially high interference, e.g. in a CRE zone, while providing the UE with time-domain measurement restriction information. Further, for LTE Release 11, advanced receivers based on Minimum Mean Square Error-Interference Rejection Combining (MMSE-IRC) with several covariance estimation techniques and interference-cancellation-capable receivers are currently being studied. In the future, even more complex advanced receivers such as advanced receivers based on Minimum Mean Square Error-Successive Interference Cancellation (MMSE-SIC), which is capable of performing nonlinear subtractive-type interference cancellation, may be used to further enhance system performance.
Such enhanced or advanced receiver techniques generally may benefit all deployments where relatively high interference of one or more signals is experienced when performing measurements on radio signals or channels transmitted by radio nodes or devices, but are particularly useful in heterogeneous network deployments. However, these techniques involve additional complexity, e.g., may require more processing power and/or more memory. Due to these factors, a UE equipped with an enhanced or advanced receiver may only use the interference handling technique(s) (i.e., the interference mitigating feature(s)) of the receiver only on specific signals or channels. For example, a UE may apply an interference mitigation or cancellation technique only on the data channel. In another example, a more sophisticated UE may apply interference mitigation on the data channel as well as on one or two common control signals. Examples of common control signals are reference signals, synchronization signals, and the like.
It should be noted that the terms “enhanced receiver” and “advanced receiver” are used interchangeably herein. Further, an enhanced, or advanced, receiver may also be referred to herein as an interference mitigation receiver, an interference cancellation receiver, an interference suppression receiver, an interference rejection receiver, an interference aware receiver, an interference avoidance receiver, or the like. In general, an enhanced, or advanced, receiver is a receiver capable of improving performance by performing one or more interference handling techniques to fully or partly eliminate interference arising from at least one interference source. The interference is generally the strongest interference signal(s) from an interference source(s), where the strongest interference signal(s) are generally interference signal(s) from a neighboring cell(s). Further, the interference handling technique(s) performed by the enhanced, or advanced, receiver may include, for example, interference cancellation, interference suppression, puncturing or interference rejection combining, or the like, or any combination thereof. Hereinafter, the term “enhanced receiver” is utilized to refer to all variants of an enhanced, or advanced, receiver.
In order to measure a quality of a received signal, LTE has standardized the following UE power-based measurements:                received signal strength (i.e., RSRP) and quality (i.e., RSRQ),        inter-Radio Access Technology (RAT) Universal Terrestrial Radio Access (UTRA) received signal strength and quality,        inter-RAT Global System for Mobile Communications (GSM) received signal strength, and        inter-RAT Code Division Multiple Access (CDMA) 2000 received signal strength.The measurements are discussed below in more detail. The RSRQ measurement definition has been additionally adapted in scenarios with high aggressor interference to better reflect interference conditions in subframes indicated for measurements (i.e., when eICIC is used when measurement resource restriction patterns are configured). Currently in LTE, the interference estimated by the UE (e.g., RSSI) is not signaled to the network. However, RSSI may be derived from the reported RSRQ and RSRP measurements, if they have been estimated in the same time intervals.        
The measurements described above are typically used for mobility purposes or a Self-Optimizing Network (SON), but the measurements may additionally or alternatively be used for other purposes, e.g., Minimization of Drive Tests (MDT), positioning, inter-cell interference coordination, power control, etc. Also, there are other quality measurements that reflect the received interference conditions, e.g.:                the quality measurement used for RLM as specified in 3GPP TS 36.133: For this quality measurement, the UE monitors the downlink link quality based on a cell-specific or other reference signal in order to detect the downlink radio link quality of the serving or Primary Cell (PCell), wherein the downlink link quality measurement for RLM purposes incorporates signal strength of the measured signal and total received interference;        Signal-to-Interference-Plus-Noise Ratio (SINR) and/or Signal-to-Noise Ratio (SNR); and        signal quality measurements in positioning subframes or low-interference subframes such as that described in, for example, PCT Patent Application Publication No. WO 2011/097760 entitled SIGNAL MEASUREMENTS FOR POSITIONING, SIGNALLING MEANS FOR THEIR SUPPORT AND METHODS OF UTILIZING THE MEASUREMENTS TO ENHANCE POSITIONING QUALITY IN LTE, filed Feb. 12, 2010 and published on Aug. 18, 2011 as well as PCT Patent Application Publication No. WO 2011/099910 entitled METHODS AND ARRANGEMENTS FOR PERFORMING MEASUREMENTS IN A WIRELESS COMMUNICATION NETWORK FOR POSITIONING OR FOR ENABLING LOCATION-BASED SERVICES, filed Oct. 6, 2010 and published on Aug. 18, 2011, both of which are hereby incorporated herein by reference with respect to their teachings on signal quality measurements in positioning subframes or low-interference subframes.        
In regard to measurements without eICIC, RSRP and RSRQ are two intra-RAT measurements of signal power and quality, respectively. In LTE, RSRP is defined as a linear average over power contributions (in Watts) of resource elements that carry cell-specific reference signals within a considered measurement frequency bandwidth. The cell-specific reference signals R0 according 3GPP TS 36.211 are used for RSRP determination. If the UE can reliably detect that R1 is available, the UE may use R1 in addition to R0 to determine RSRP. The reference point for RSRP measurement is the antenna connector of the UE. If receiver diversity is in use by the UE, the reported RSRP value is not to be lower than the corresponding RSRP of any of the individual diversity branches. The RSRP measurement is applicable for RRC_IDLE intra-frequency, RRC_IDLE inter-frequency, RRC_CONNECTED intra-frequency, and RRC_CONNECTED inter-frequency. Therefore, the UE should be capable of using RSRP in all these RRC states and measurement scenarios.
In LTE, RSRQ is defined as a ratio N×RSRP/(Evolved Universal Terrestrial Radio Access (E-UTRA) carrier RSSI), where N is the number of resource blocks of the E-UTRA carrier Received Signal Strength Indicator (RSSI) measurement bandwidth. The measurements in the numerator and denominator are made over the same set of resource blocks. E-UTRA carrier RSSI comprises a linear average of a total received power (in Watts) observed only in Orthogonal Frequency Division Multiplexing (OFDM) symbols containing reference symbols for antenna port 0 in the measurement bandwidth over a number N of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise, etc. The reference point for RSRQ measurements is the antenna connector of the UE. If receiver diversity is in use by the UE, the reported RSRP value is not to be lower than the corresponding RSRQ of any of the individual diversity branches. The RSRP measurement is applicable for RRC_IDLE intra-frequency, RRC_IDLE inter-frequency, RRC_CONNECTED intra-frequency, and RRC_CONNECTED inter-frequency. Therefore, the UE should be capable of using RSRP in all these RRC states and measurement scenarios.
Whereas RSRP and RSRQ are two intra-RAT measurements without eICIC, UTRA FDD Common Pilot Channel (CPICH) Received Signal Code Power (RSCP), UTRA FDD Secondary Pilot Channel (SPICH) Energy per Chip/Noise Spectral Density (Ec/No), GSM carrier RSSI, UTRA TDD Primary Common Control Physical Channel (P-CCPCH) RSCP, CDMA2000 1x Round Trip Time (RTT) Pilot Strength, and CDMA2000 High Rate Packet Data (HRPD) Pilot Strength are inter-RAT measurements without eICIC. More specifically, UTRA FDD CPICH RSCP is the received power on one code measured on the Primary CPICH. The reference point for the RSCP is the antenna connector of the UE. If Tx diversity is applied on the Primary CPICH, the received code power from each antenna is separately measured and summed together in Watts to a total received code power on the Primary CPICH. If receiver diversity is in use by the UE, the reported value is not to be lower than the corresponding CPICH RSCP of any of the individual receive antenna branches. The UTRA FDD CPICH RSCP measurement is applicable for RRC_IDLE inter-RAT and RRC_CONNECTED inter-RAT. Therefore, the UE should be capable of using UTRA FDD CPICH RSCP in all these RRC states and measurement scenarios.
UTRA FDD CPICH Ec/No is the received energy per chip divided by the power density in the band. If receiver diversity is not in use by the UE, the CPICH Ec/No is identical to CPICH RSCP/UTRA Carrier RSSI. Measurement is performed on the Primary CPICH. The reference point for the CPICH Ec/No is the antenna connector of the UE. If Tx diversity is applied on the Primary CPICH, the received energy per chip (Ec) from each antenna is separately measured and summed together in Watts to a total received chip energy per chip on the Primary CPICH, before calculating the Ec/No. If receiver diversity is in use by the UE, the measured CPICH Ec/No value is not to be lower than the corresponding CPICH RSCPi/UTRA Carrier RSSIi of receive antenna branch i. The UTRA FDD CPICH Ec/No measurement is applicable for RRC_IDLE inter-RAT and RRC_CONNECTED inter-RAT. Therefore, the UE should be capable of using UTRA FDD CPICH Ec/No in all these RRC states and measurement scenarios.
GSM carrier RSSI is an RSSI for the wide-band received power within the relevant channel bandwidth. Measurement is performed on a GSM Broadcast Control Channel (BCCH) carrier. The reference point for the RSSI is the antenna connector of the UE. The GSM carrier RSSI measurement is applicable for RRC_IDLE inter-RAT and RRC_CONNECTED inter-RAT. Therefore, the UE should be capable of using GSM carrier RSSI in all these RRC states and measurement scenarios.
UTRA TDD P-CCPCH RSCP is defined as the received power on P-CCPCH of a neighbor UTRA TDD cell. The reference point for the RSCP is the antenna connector of the UE. The UTRA TDD P-CCPCH RSCP measurement is applicable for RRC_IDLE inter-RAT and RRC_CONNECTED inter-RAT. Therefore, the UE should be capable of using UTRA TDD P-CCPCH RSCP in all these RRC states and measurement scenarios.
CDMA2000 1x RTT Pilot Strength is defined in section 5.1.10 of 3GPP TS 36.214. CDMA2000 HRPD Pilot Strength is defined in section 5.1.11 of 3GPP TS 36.214. The CDMA2000 1x RTT Pilot Strength and CDMA2000 HRPD Pilot Strength measurements are applicable for RRC_IDLE inter-RAT and RRC_CONNECTED inter-RAT. Therefore, the UE should be capable of using CDMA2000 1x RTT Pilot Strength and CDMA2000 HRPD Pilot Strength in all these RRC states and measurement scenarios.
The measurements above are made without eICIC. The following measurements are made with eICIC. In the current LTE standard, RSSI measurements with eICIC are averaged over all symbols of a subframe, unlike RSSI measurements without eICIC. Specifically, with eICIC, RSRP is defined as the ratio N×RSRP/(E-UTRA carrier RSSI), where N is the number of resource blocks of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator are made over the same set of resource blocks. E-UTRA Carrier RSSI comprises the linear average of the total received power (in Watts) observed only in OFDM symbols containing reference symbols for antenna port 0 in the measurement bandwidth over N number of resource blocks by the UE from all sources, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise, etc. With respect to eICIC, if higher-layer signaling indicates certain subframes for performing RSRQ measurements, then RSSI is measured over all OFDM symbols in the indicated subframes. The reference point for the RSRQ is the antenna connector of the UE. If receiver diversity is in use by the UE, the reported value is not to be lower than the corresponding RSRQ of any of the individual diversity branches.
A wideband RSRQ (aka wide bandwidth RSRQ) is similar to the RSRQ described above except that the former (wideband RSRQ) is measured over a measurement bandwidth larger than six resource blocks. That means a wideband RSRQ has to meet requirements corresponding to measurement bandwidth of larger than six resource blocks. The wideband RSRQ is performed by the UE when explicitly indicated by the network, e.g. in some specific deployment scenarios.
The measurements discussed above are generally used for mobility purposes. Other measurements are defined for purposes other than mobility. Some examples are RLM related measurements, CSI measurements, measurements related to signal quality in general, and interference measurements. In regard to RLM related measurements, the UE also performs measurements on the serving cell (or primary cell) in order to monitor the serving cell performance. The performance of these measurements is referred to as RLM, and the measurements are referred herein to as RLM related measurements.
For RLM, the UE monitors the downlink link quality based on the cell-specific reference signal in order to detect the downlink radio link quality of the serving or primary cell. In principle, the downlink link quality can also be monitored also on other types of reference signals, e.g. Demodulation Reference Signal (DMRS), Channel State Information-Reference Signal (CSI-RS), etc. The downlink link quality measurement for RLM purposes incorporates signal strength of the cell-specific reference signal (or any other signal used for measurement) and total received interference. Therefore, RLM measurement is also regarded as a quality measurement.
In order to detect out of sync and in sync conditions, the UE compares the estimated quality with defined thresholds Qout and Qin, respectively. The thresholds Qout and Qin are defined as the levels at which the downlink radio link cannot (Qout) and can (Qin) be reliably received and correspond to 10% and 2% block error rate of a hypothetical PDCCH transmission, respectively. In non-Discontinuous Reception (non-DRX), downlink link quality for out of sync and in sync are estimated over evaluation periods of 200 milliseconds (ms) and 100 ms, respectively. In DRX, downlink link quality for out of sync and in sync are estimated over the same evaluation periods, which scale with the DRX cycle, e.g. a period equal to 20 DRX cycles for DRX cycle greater than 10 ms and up to 40 ms. In non-DRX, the out of sync and in sync statuses are assessed by the UE in every radio frame. In DRX, the out of sync and in sync statuses are assessed by the UE once every DRX.
In addition to filtering on the physical layer (i.e., evaluation period), the UE also applies higher layer filtering based on network configured parameters. This increases the reliability of radio link failure detection and thus avoids unnecessary radio link failure and consequently RRC re-establishment. The higher layer filtering for radio link failure and recovery detection would in general comprise the following network controlled parameters:                hysteresis counters, e.g. N310 and N311 out of sync and in sync counters respectively, and        timers, e.g. T310 Radio Link Failure (RLF) timer.For example the UE starts the timer T310 after N310 consecutive Out-Of-Sync (OOS) detections. The UE stops the timer T310 after N311 consecutive In-Sync (IS) detections. The transmitter power of the UE is turned off within 40 ms after the expiry of the timer T310. Upon expiry of the timer T310, the UE starts the timer T311. Upon expiry of the timer T311, the UE initiates RRC re-establishment phase during which it reselects a new strongest cell. In High Speed Packet Access (HSPA), similar concepts called OOS and IS detection are carried out by the UE. The higher layer filtering parameters (i.e., hysteresis counters and timers) are also used in HSPA. There is also RLF and eventually RRC re-establishment procedures specified in HSPA.        
In LTE, CSI measurements are performed and reported by the UE. They are defined to facilitate processes such as, for example, scheduling, link adaptation, selection of antenna transmission mode, etc. CSI measurements are typically performed on CRS that are transmitted in the downlink in every subframe. The network can request both periodic and aperiodic CSI reports from the UE. In LTE Release 8/9, both periodic and aperiodic reports are based on CRS. In LTE Release 10, the CSI report can also be based on CSI-RS, which is used for transmission mode 9. There are three main types of CSI reports in LTE:                Rank Indicator (RI): RI is a recommendation to a base station regarding how many layers in the downlink transmission must be used. The RI is only one value which means that the recommended rank is valid across the whole bandwidth.        Precoder Matrix Indicator (PMI): PMI indicates the recommended precoder matrix that must be used in the downlink transmission. The recommended precoder matrix can be frequency-selective.        Channel Quality Indicator (CQI): CQI shows the highest modulation and coding that can be used for downlink transmission. CQI can be frequency-selective, which means that multiple CQI reports can be sent for different parts of the bandwidth. However, the indication does not explicitly comprise the signal quality metric (e.g., RSRQ).        
Regarding signal quality in general, the UE may estimate a signal quality such as SNR, SINR, etc. for various purposes such as for monitoring quality of different physical channels, channel estimation, etc. These measurements are also quality measurements as they incorporate an interference component.
As for interference measurements, currently in LTE, the interference estimated by the UE (e.g., RSSI) is not signaled to the network. However, the interference may be derived from the reported RSRQ and RSRP measurements, if they have been estimated in the same time intervals.
To enhance peak rates within a technology, multi-carrier or carrier aggregation solutions are known. Each carrier in multi-carrier or carrier aggregation system is generally termed as a Component Carrier (CC) or sometimes it is also referred to as a cell. In simple words the CC means an individual carrier in a multi-carrier system. The term Carrier Aggregation (CA) is also called (e.g., interchangeably called) “multi-carrier system,” “multi-cell operation,” “multi-carrier operation,” “multi-carrier” transmission, and/or reception. This means the CA is used for transmission of signaling and data in the uplink and downlink directions. One of the CCs is the Primary Component Carrier (PCC) or simply primary carrier or even anchor carrier. The remaining ones are called Secondary Component Carrier (SCC) or simply secondary carriers or even supplementary carriers. Generally the primary or anchor CC carries the essential UE specific signaling. The PCC exists in both uplink and direction CA. The cellular communications network may assign different primary carriers to different UEs operating in the same sector or cell.
Therefore the UE has more than one serving cell in downlink and/or in the uplink: one primary serving cell and one or more secondary serving cells operating on the PCC and the SCC respectively. The serving cell is interchangeably called as a PCell or Primary Serving Cell (PSC). Similarly the secondary serving cell is interchangeably called a Secondary Cell (SCell) or Secondary Serving Cell (SSC). Regardless of the terminology, the PCell and the SCell(s) enable the UE to receive and/or transmit data. More specifically the PCell and the SCell exist in the downlink and the uplink for the reception and transmission of data by the UE. The remaining non-serving cells on the PCC and SCC are called neighbor cells.
The CCs belonging to the CA may belong to the same frequency band (aka intra-band CA) or to different frequency band (inter-band CA) or any combination thereof (e.g., two CCs in band A and one CC in band B). Furthermore, the CCs in intra-band CA may be adjacent or non-adjacent in frequency domain (aka intra-band non-adjacent CA). A hybrid CA comprising of any two of intra-band adjacent, intra-band non-adjacent, and inter-band is also possible. Using CA between carriers of different technologies is also referred to as “multi-RAT CA” or “multi-RAT-multi-carrier system” or simply “inter-RAT CA.” For example, the carriers from Wideband Code Division Multiple Access (WCDMA) and LTE may be aggregated. Another example is the aggregation of LTE FDD and LTE TDD, which may also be interchangeably called a multi-duplex CA system. Yet another example is the aggregation of LTE and CDMA2000 carriers. For the sake of clarity the CA within the same technology as described can be regarded as “intra-RAT” or simply “single RAT” CA.
The CCs in CA may or may not be co-located in the same site or radio network node (e.g., radio base station, relay, mobile relay, etc.). For instance the CCs may originate (i.e., be transmitted/received) at different locations (e.g. from non-located base stations, or from base stations and RRH, or at Remote Radio Units (RRUs)). The well known examples of combined CA and multi-point communication are Distributed Antenna Systems (DAS), RRH, RRU, Coordinated Multi-Point (CoMP), multi-point transmission/reception, etc. The proposed solutions also apply to the multi-point CA systems but also multi-point systems without CA. The multi-carrier operation may also be used in conjunction with multi-antenna transmission. For example signals on each CC may be transmitted by the eNB to the UE over two or more antennas. The embodiments apply to each CC in CA or combination of CA and CoMP scenario.
The use of enhanced receivers and mixtures of enhanced receivers and conventional receivers in a cellular communications network result in new problems associated with some, if not all, of the measurements discussed above. As such, there is a need for systems and methods for addressing these issues.